I picked up a small loose cobble from the shore at Ravenscar, Robin Hood's Bay. It could be locally derived or from the glacial till, but I'm left with this issue...
The ammonite, sandwiched between two pecten like bivalves is almost completely covered. It's the bivalve that I mostly need help with.
The ammonite has ribs that curve forward at the venter but don't reach the keel. The keel is eroded, but is narrow and without lateral grooves. Comparing it with a Grammoceras I have, I think it's that. If so, its upper Lias.
Looking in the Palass guide, the most similar bivalve mat